To our knowledge, filtering systems have not been heretofore provided which can be added easily to already fully constructed buses and which efficiently remove a wide variety of pollutants which gain entry to the bus interior from outside the bus or from the bus lavatory. These pollutants include fecal and urine odor-producing pollutants and dust, soot, pollen, bacteria, pathogenic mole spores, and dust associated viruses. Conventional filters used heretofore in buses are filters for removing primarily large or heavy solid materials such as soot, pollen, ragweed, dust and the like. Odors have been dealt with primarily by odor-masking rather than odorproducing particle-removing means.